Personal communication devices are becoming more widely adopted by the public. Such devices as cellular phones, personal digital assistants, and laptop computers give users a variety of mobile communications and computer networking capabilities. These devices are increasingly able to communicate using a wide variety of digital multimedia formats, include voice, music, video, text messaging, etc.
One important standard that has allowed providing digital multimedia to mobile and other computing devices is the Session Initiation Protocol (SIP). SIP is a signaling protocol that assists digital devices in establishing end-to-end multimedia sessions. SIP provides features that resemble those provided by the Public Switch Telephone Network (PSTN) as well as Internet protocols such as Transmission Control Protocol/Internet Protocol (TCP/IP) and Hypertext Transfer Protocol (HTTP).
SIP operates similarly to HTTP, in that it is a text based message protocol operating on a well-known network port. From the terminal's perspective, SIP is different than HTTP because the terminal must have a listening process to be notified of incoming communications. In contrast, a web browser utilizing HTTP is purely a client the browsers initiates connections to listening servers at the users request, and does not listen for incoming connections.
As devices such as mobile phones and personal digital assistants (PDAs) become more sophisticated, these devices will allow the users to run more multimedia aware applications simultaneously. It is likely that these applications will utilize the SIP protocol. Therefore, there may be a high degree of redundancy, as each application will include its own SIP protocol stack. Having multiple SIP aware applications could cause confusion on the part of the users, as there may be contention for well-known TCP/IP listening ports on the device. This contention could lead to errors and the requirement that users specially configure software to work simultaneously. This is disadvantageous because users generally do not understand concepts such as TCP/IP ports, and may cause problems if an alternate, well-known port (such as one for HTTP or telnet) is selected by the user to receive SIP.
What is needed is a way to provide SIP functionality to multiple client applications on a communications device. The present invention addresses these and other needs, and offers other advantages over prior art approaches.